Magenta couplers for use in commercial photographic materials, including films and papers, are usually drawn from the pyrazolone and pyrazolotriazole classes, in view of the stability of these compounds in raw-stock and their rapid and efficient reaction with oxidized color developers. Dyes derived from commercial pyrazolone and pyrazolotriazole magenta couplers also have acceptable spectrophotometric curve shapes. Magenta couplers are described in such representative patents and publications as: U.S. Pat. Nos. 2,311,082, 2,343,703, 2,369,489, 2,600,788, 2,908,573, 3,062,653, 3,152,896, 3,519,429, and "Farbkuppler-eine Literature-Ubersicht," published in Agfa Mitteilungen, Band III, pp. 126-156 (1961). Preferably such couplers are pyrazolones, pyrazolotriazoles, or pyrazolo-benzimidazoles.
It is also known to use image-modifying couplers which release development inhibitors on reaction with oxidized developer to provide one or more functions such as contrast or curve shape control, sharpness enhancement, granularity reduction and color correction via interlayer effects. The image-modifying couplers include development inhibitor releasing (DIR) couplers from which inhibitor is released directly as a coupling-off group.
Examples of DIR couplers are described in U.S. Pat. Nos. 3,137,578; 3,148,022; 3,148,062; 3,227,554; 3,384,657; 3,379,529; 3,615,506; 3,617,291; 3,620,746; 3,733,201; 4,049,455; 4,095,984; 4,126,459; 4,149,886; 4,150,228; 4,211,562; 4,248,962; 4,259,437; 4,362,878; 4,409,323; 4,477,563; 4,782,012; 4,962,018; 4,500,634; 4,579,634; 4,579,816; 4,607,004; 4,618,571; 4,678,739; 4,746,600; 4,746,601; 4,791,049; 4,857,447; 4,865,959; 4,880,342; 4,886,736; 4,937,179; 4,946,767; 4,948,716; 4,952,485; 4,956,269; 4,959,299; 4,966,835; 4,985,336 as well as in patent publications GB 1,560,240; GB 2,007,662; GB 2,032,914; GB 2,099,167; DE 2,842,063, DE 2,937,127; DE 3,636,824; DE 3,644,416 as well as the following European Patent Publications: 272,573; 335,319; 336,411; 346,899; 362,870; 365,252; 365,346; 373,382; 376,212; 377,463; 378,236; 384,670; 396,486; 401,612; 401,613.
Such compounds are also disclosed in "Developer-Inhibitor-Releasing (DIR) Couplers for Colour Photography", C. R. Barr. J. R. Thirtle and P. W. Vittum in Photographic Science and Engineering, Vol. 13, p.174 (1969), incorporated herein by reference.
The image-modifying couplers also include development inhibitor anchiomerically releasing (DIAR) couplers from which inhibitor is released from a coupling-off group after a timed delay which results from an additional reaction step. This delay permits control over such parameters as time of release, rate of release and rate of diffusion of the PUG without altering the nature of the PUG itself.
Compounds having a nitrogen-linked coupling-off group which release PUGs after a delay are known from JP59-206834. The PUG is released by reaction of the electrophile (E) with the nucleophile (Nu) which is formed when A (coupler moiety) reacts with oxidized developer: EQU A-Nu-PUG-E
With compounds of this type, the PUG remains attached to the fragment of the Nu which was bonded to A. This makes it impossible to vary independently the PUG and the characteristics of the anchiomeric release mechanism.
U.S. Pat. No. 4,248,962 also describes the imagewise release of PUGS, from coupler compounds in photographic elements and processes, the couplers being represented by the structure: EQU COUP-TIME-PUG
where COUP is a coupler moiety and TIME is a timing group, the coupler moiety being any moiety which will react with oxidized color developing agent to release the -TIME-PUG group. This patent is primarily concerned with couplers in which the nucleophile, Nu, attached to COUP, and the electrophile, E, attached to PUG, are spatially related by a linking group X, such as TIME=Nu-X-E. After displacement of Nu from COUP, an intramolecular nucleophilic displacement reaction occurs with the formation of a ring and release of the PUG.
Representative groups for Nu are listed and from the numerous examples it is clear that the linking atom to the COUP is in practice either a sulfur atom or preferably an oxygen atom. However there are problems associated with the use of aryloxy coupling-off groups attached to photographic couplers which give magenta dyes on reaction with oxidized developer. Thus the compounds are either unstable (e.g. aryloxypyrazolones) or difficult to make (e.g. aryloxypyrazolotriazoles). For compounds with an S-linking group, the intra-molecular reaction subsequent to reaction of the coupler with oxidized developer does not proceed satisfactorily.
Moreover the general method of synthesis described in the afore-mentioned patent, is sequential, i.e. all the molecule must be taken through each of a series of steps which leads to a cumbersome and lengthy process.
Problem to be Solved by Invention PA0 the reaction of a compound of formula (II) ##STR3## or (ii) when R.sub.1 and R2 are the same: PA0 the reaction of a compound of formula (IV) ##STR4## with a compound of formula (III) EQU LG-R.sub.1 PA0 wherein R.sub.1, R.sub.2, Ln and COUP are as hereinbefore defined and LG is a leaving group and at least R.sub.1 =X-E-PUG, wherein X is a linking group, E is an electrophilic center and PUG is a photographically useful group. PA0 Advantageous Effect of the Invention
There is therefore a need to provide compounds having an N-linking group which overcome the disadvantages associated with the aryloxy and arylmercapto compounds and to further provide a method for their preparation and in particular one in which the method is convergent, i.e. part of the molecule can be made using one sequence of reactions, the other part of the molecule can be made by using another sequence of reactions and then the two parts combined in a single reaction. This means that not all of the molecule has to go through each of the steps.